A normal door latch only extends about 1/2 inch from the front edge of the door. When consideration is given to the normal space between the door frame and the outer edge of the door, there may only be about 3/8 inch of the latch which may penetrate the opening in the striker plate. With this minimal engagement, a good strong kick in the center of the door may bow the door so that the latch is released; or a simple prying tool may be employed to release the door, and permit undesired entry. In order to avoid this problem, many people now use a supplemental deadbolt which is normally key-operated, and which extends into the door frame a full inch. This precludes opening of the door by the simpler expedients mentioned hereinabove. It is also noted in passing that some insurance companies will give reduced rates to home owners who equip their homes with deadbolts on the exterior doors, and certain other safety equipment.
One prior proposed arrangement for a combination latch and deadbolt lock is disclosed in U.S. Pat. No. 4,255,953, granted Mar. 17, 1981. This prior patent includes two modes of operation. In one mode of operation the latch only extends for the usual 1/2 inch, and the door operates in all respects like a normal door. Then, through the special use of a key or other actuation arrangements, the conventional type of latch is extended by an additional half an inch so that it acts in the manner of a deadbolt. It is noted, however, that although the latch and deadbolt functions are accomplished by this single device, the deadlock can be actuated from the outside of a door in which it is installed only by inserting and turning a key.
The simple action of inserting and turning a key, as important as it is in providing the greatly increased security of a deadbolt lock when compared to a conventional latch, is one which many people are unwilling to do regularly. Perhaps the best illustration of this fact is that the great majority of hotel and motel rooms can be locked from the outside only by closing the door. Deadbolt locks are generally provided, but they can be locked only from the inside. Thus, in spite of the small extra cost of installing deadbolt locks which can be locked from both sides of the door in order to provide much greater security, to the benefit of both management and guests of hotels and motels, this cost is evidently considered excessive in view of the evident low probability that the outside deadlocking arrangements would be used. Similarly, this reluctance to use a key to lock a door from the outside applies as well to people locking the door of their homes.
Accordingly, a principal object of the present invention is to provide an improved combination latch and deadbolt in a single inexpensive unit which will fit and conventionally cut doors, and which can be locked from the outside by merely pulling the door closed, thus providing the convenience of a conventional latch as well as the security of a deadbolt.